U.S. Pat. No. 4,613,641 (BYK-Chemie GmbH) and the corresponding DE 34 27 208 describe siloxanes which contain polyester groups as flow-promoting additives for coating materials and molding compositions, in which the polyester groups are bonded to the silicon atoms of the siloxane via divalent radicals and in which one siloxane unit may not have more than one polyester chain. U.S. Pat. No. 4,985,511 (University of Florida) describes carboxy-functional siloxanes onto which pivalolacetone is polymerized by ring-opening polymerization. In this polymerization, only side chains with acid or ester terminal groups are obtained. Furthermore, in Polym, Prepr., Am. Chem. Soc., Div. Polym, Chem. 26 (1985) No. 1, 251-2 (J. S. Riffle), .epsilon.-caprolactone is polymerized onto .alpha.,w-bis(4-hydroxybutyl)polydimethylsiloxane to produce block copolymers which are converted into polyurethanes.